A health monitoring system (HMS) in general monitors one or more parameters corresponding to the health of a system. Such parameters may pertain to the system environment, which are typically represented as analog data signals that may also be referred to as raw data, raw analog data signals, analog information signals, analog data streams, or analog information streams. Exemplary parameters that are represented by such analog data signals include temperature, humidity, radioactivity, PH, etc. Such parameters may also be represented by analog data signals relating to physical properties of a system, for example, loading, stress, strain, acceleration, etc. Certain properties may be measured relative to one or more directions or axes.
FIG. 1a illustrates an exemplary prior art HMS 100 for processing a raw analog data signal. Referring to FIG. 1a, a sensor 102 outputs an analog data signal 104 that is conditioned by a signal conditioning circuit (or conditioner) 106 to produce a conditioned analog data signal 108 that is inputted into an analog-to-digital converter circuit (or A/D converter) 110. Optionally, analog data signal 104 can be inputted directly into the analog-to-digital converter circuit 110. The analog-to-digital converter circuit 110 includes a sample-and-hold circuitry and provides a digital data signal 120 to a processor 112. The processor 112 stores and retrieves digital data signal 120 values using a memory 116 and interfaces with a clock 118. The conditioned analog data signal 108 may also be input into a raw analog data trigger device (or trigger) 114 that compares the conditioned analog data signal 108 to a determined, or established, threshold value, or any other comparison criteria, and triggers a raw analog data event signal 122 to processor 112 when the conditioned analog data signal 108 is greater than or equal to the threshold value or when the comparison criteria is met in any manner.
The conditioning circuitry 106 may comprise an operational amplifier used to amplify analog data signal 104 to an appropriate voltage required for proper operation of the analog-to-digital converter circuit 110. Generally, the conditioning circuitry 106 may comprise circuitry intended for amplification, filtering, converting, and any other processes required to make sensor output suitable for conversion to a digital format. A raw analog data trigger device 114 would typically comprise a comparator. As such, the prior art health monitoring system can be described as a system that produces analog data signals corresponding to sensor measurements, conditions the analog data signals to enable conversion to a digital format, and converts the analog sensor measurements to digital sensor measurements, which are stored in memory for post processing. The prior art health monitoring system may also trigger an event if an analog sensor measurement meets or exceeds an established threshold. It should be noted that in FIG. 1a, the raw analog data trigger device 114, raw analog data event signal 122, the input of analog data signal 104 into analog-to-digital converter circuit 110, and the input of conditioned analog data signal 108 into raw analog data trigger device 114 are depicted using dashed lines to indicate that they are optional. Dashed lines are also used in several subsequent figures to indicate options.
FIG. 1b illustrates an exemplary prior art health monitoring method 130 for processing a raw analog data signal. Referring to FIG. 1b, health monitoring method 130 comprises several steps intended to store individual samples of a raw analog data signal. In a first step 132, an analog data signal is obtained, for example, from a sensor. In a second step 134, which may or may not be required, the analog data signal is conditioned, for example amplified, thereby producing a conditioned analog data signal. The conditioned analog data signal is then converted in a third step 136 to a digital data value, the digital data value corresponding to a discrete sample of the analog data signal. In a fourth step 138, the digital data value is stored in a memory, for example, a hard drive. A time stamp may be stored along with each digital data value or a reference time may be associated with multiple sample values, for example, multiple samples sampled at a defined sampling rate relative to a determined reference time. An optional step 140 of method 130 is to compare the conditioned analog data signal to a threshold and, if it meets (or exceeds) the threshold, another optional step 142 is performed, which is to trigger a raw analog data event (or event). Triggering an event could be setting off an alarm, shutting down a system, varying a parameter of the system, changing the rate at which the analog data signal is being sampled, for example, increasing the sampling rate for some period of time in order to more precisely capture the aftermath of the triggered event in greater detail, or any other defined action or process.
An exemplary HMS scenario involves the monitoring of vibrations in the tail rotor of a helicopter; where it is desirable to detect operational anomalies prior to rotor failure. A typical vibration monitor used to monitor vibration in the tail rotor may sample vibrations represented by an analog data signal at the rate of 20,000 samples per second, which for a 3 hour flight corresponds to 72,000,000 samples. Clearly, the data storage and processing requirement for 3 hours of such sampled raw data is significant. Thus, long term monitoring of the health of a system using sampled raw data can require power and memory resources that are often cost prohibitive. Moreover, the huge amounts of raw data produced by an existing HMS when used for long term monitoring of the health of a system often requires significant data storage resources, and the computational resources and significant time required to process such amounts of raw data make real time assessment of the health of a system impractical to achieve under many health monitoring scenarios.
Generally, as the amount of raw analog data pertaining to the monitoring of a system increases, power storage and processing requirements also increase so it becomes more and more difficult to make a real time assessment of the health of the monitored system. Therefore, there exists a need for an improved system and method for monitoring of an analog data signal.